Rotating spool servo valve



Dec. 29, 1953 w PARKER 2,664,097

ROTATING SPOOL SERVO VALVE Filed Jan. 8, 1951 3 Sheets-Sheet l j 1Z5 .1 I

lNl/E/VT'O/l 14/4206 A. PdZKER.

Dec. 29, 1953 w, PARKER 2,664,097

ROTATING SPOOL SERVO VALVE Filed Jan. 8, 1951 3 Sheets-Sheet 5 2E TUA/V P26651126 F g: 6 ro/zasa m/n. mm m/fl IIVVdA/TOA wmae 1. meme,

Patented Dec. 29, 1953 ROTATING SPOOL SERVO VALVE Warde L. Parker, Los Angeles, Calif., ass'ignor to Northrop Aircraft, Ina, Hawthorne, Calif., a

corporation of California Application January 8, 1951, Serial No. 204,978,

1 Claim. 1

This invention relates to controls for hydraulic motors, and more particularly to a hydraulic valve as used in a system ideally suitable for full power operation of aircraft control surfaces under pilot control of the hydraulic motor valve in the system.

The trend in aircraft design is to larger, faster, and more powerful aircraft. Control surface loads have increased, and in many cases it has been desirable to resort to full power operation of the control surfaces as by the full powered hydraulic flying control system as described, for example, in U. S. application, Serial No. 23,567, filed April 27, 1948, now abandoned. The F439 U. S. Air Force jet-propelled fighter aircraft, for example, has such a full powered control system operated entirely by hydraulic power under pressure of 3,000 p. s. 1.

Means for controlling the flow or hydraulic fluid by means of sleeve and spool valve assemblies, suitable for use in aircraft control systems, are shown, described and claimed in U. S. application, Serial No. 17,624, filed March 29, 1948 by Parker, now Patent 2,631,571, and in U. S. application, Serial No. 123,375, filed October 25, 1949 by Strayer, now Patent 2,612,372, wherein hydraulic pressure fluid is metered through channels arranged to provide a predetermined flow portion by movement of an internal valve spool which is axially displaced by push-pull movement of control rod in response to manual operation by the pilot of the aircraft.

Servo valves of the type described above have proved highly satisfactory, particularly in connection with attitude control surfaces. Certain flying controls, however, are in use on current aircraft, these controls being of a type which are set and maintained for certain periods of time at predetermined angles of attack. One of these controls, the dive brake for example, may be set at a certain angle and maintained there for substantial periods of time while subjected to severe aerodynamic stresses during high speed flight. The same conditions apply when an attitude control surface is moved away from aerodynamic neutral and maintained away from neutral for prolonged periods for trimming purposes. Under such conditions in servo valves of the general type referred to, there may be a tendency to build-up a binding force in the valve such that the pilot is required to exert an increasingly greater effort to displace the valve spool in the servo valve. Normally, in full power systems, the valve spool is controlled by the pilot through cables deliberately made as light as possible to handie only normal'valve spool friction plus a small safety factor. Ordinarily the spool friction value is on the order of only 1.5 pounds.

It has been found, however, that under certain load conditions of the control system maintained for extended periods, the spool friction value may rise to a point where thirty pounds or more may be required to move it. When the pilot is required to operate a servo valve wherein the force has increased to thirty pounds, for example, undesirable operating handle load and cable stretch will result. When the valve spool finally moves, under the abnormal force condition, the spool moves beyond the limit desired and over-controls the control surface actuated by the system. Over-control of any control surface can, of course, be highly undesirable.

The exact reason for the build-up of the binding forces in the valve is not at present fully known, but many experimental tests have shown that with valves such as described herein and in the applications cited above, spool movement forces can rise from a normal of 1.5 pounds to over thirty pounds in time periods on the order of fifteen minutes, with a source pressure of 3,090 p. s. 1.

It is, therefore, one of the objects of the present invention to provide a servo valve ideally suitable for use in connection with a hydraulic motor cylinder operating an airplane control surface, for example, which will have a pilot operating force of substantially uniform value at all times, and under all surface loads even if prolonged.

Another object of the present invention is to provide means for preventing the increase of binding forces in a servo valve that may occur during conditions where the binding forces in the valve would normally tend to increase.

Other objects will become more apparent as the description continues.

Briefly, the invention includes a hydraulic valve of the general type shown, described and claimed in the applications cited above, suit able for operation, for example, of a servo motor connected to move an airplane control surface under aerodynamic loads. The valve, operate-d by the pilot by a push-pull motion of the valve spool, is provided with means for continuously rotating the valve spool and the present invention is primarily concerned with the provision of an improved valve structure of the kind described. Preferably, the means for rotating the valve spool is a hydraulic motor, and also it is preferred to place this motor inside the valve casing so that the seal between spool and easing will not wear 3 or produce rotating friction. With the motor located within the valve casing, the energy for spool rotation is conveniently obtained by utilizing a part of the energy contained in the hydraulic fluid suppiled under pressure to the valve for operation of the controlled hydraulic motor.

The present ivnention will be more clearly understood by reference to the drawings, in which:

Figure 1 is a simplified diagrammatic view in perspective of a valve with the spool rotated by an electric motor.

Figure 2 is a simplified diagrammatic view in perspective of a valve with the spool rotated by a hydraulic motor of the gear type.

Figure 3 is a longitudinal sectional view showing one preferred form of the present invention with the valve spool in neutral position.

Figure 4 is a cross-sectional view as indicated by line l4 in Figure 3.

Figure 5 is a cross-sectional view as indicated by line 5-5 in Figure 3.

Figure 6 is a somewhat diagrammatic cutaway view in perspective of a preferred rotating valve spool motor.

Figure 7 is a side view of the valve sleeve partially cut away to show the metering flow hole pattern.

Figure 8 is a somewhat schematic longitudinal sectional view of the rotating spool valve connected to a hydraulic motor cylinder with the spool at one end of its stroke.

Figure 9 is a somewhat diagrammatic longitudinal sectional view with the spool in neutral position.

Figure 10 is a somewhat diagrammatic longitudinal sectional view with the spool at the other end of its stroke.

First, the hydraulic control valve of the speciflc construction shown in detail in Figure 3 is very schematically shown in the simplified views in Figures 1 and 2 with details of the valve spools and casings being omitted to merely demonstrate two ways in which continuous rotation of a valve spool in a valve casing can be carried into effect. In Figure 1, a valve spool a is slidably enclosed in a valve body b positioned between two end bearing couplings c and d which allow the spool a to freely rotate while being moved axially by a push-pull control rod e attached at one end of the valve body b, hereinafter called the forward end, to the end bearing coupling 0 and locked therein by means of a front pin 1. At the other end of the spool a, hereinafter called the rear end, an idler rod 9 is fastened into the end bearing coupling :1 by rear pin j and extends into a hollow shaft h and is slidably fastened therein by a rod pin 1' extending through the idler rod g into an elongated slot in the shaft h. The shaft h is provided with a gear k at the outer end thereof, which meshes with another gear 2 on a power shaft m which passes through a seal 11 in the valve body 12 and into an electric motor 0, for example. Operation of motor 0, connected to power supply B, will rotate the valve spool a without interfering with the axial movement of the spool a in the valve casing b. Such rotation is to be performed continuously during the use of the valve so that the force required to move the spool in the casing for fluid control purposes will remain constant at all times.

Under certain conditions, such as long flights of the airplane, the valve may be in use for many hours. Under these circumstances, to avoid excessive wear on seal 11. due to the continuous rotation of power shaft m, it may be desirable to place the motor inside casing b and thus avoid such seal wear.

Figure 2 shows the installation of a hydraulic motor p, which is mounted within the valve body 17. The spool a is positioned between two end bearing couplings c and d, the same as in Figure l. The idler rod enters a hollow shaft h and is slidably fastened therein by means of a pin 2' extending through its section into an elongated slot 9'. The shaft it enters the motor housing p formed within valve body b and connects to the gear assembly q. Pressure fluid enters the motor 19 at an inlet r and the fluid is exhausted by outlet s and return line t. As will be brought out later, it is convenient to take fluid under pressure to operate the motor 1) from the same source as is to be controlled by movement of spool a and return the exhausted fluid to the same return line as used by the valve. Such an arrangement is ghown in preferred form and in detail in Figures In Figure 3, a valve body [0 is provided with a pressure fluid inlet II, a fluid outlet (2, a left return chamber [4 and a right return chamber 5 connected by a smooth valve body bore i6, and cylinder operating ports I! and I9. Four diagonally opposed longitudinal fluid return passages 20 (best shown in Figures 4 and 5), enter valve body It) at the right end thereof, intersecting right return chamber l5 as they pass therethrough and continue axially through valve body I0, intersecting and terminating slightly beyond left return chamber l4, returning fluid to chamber M from return chamber [5. Return chambers l4 and I5 are each counter-bored at diagonally opposed points to form a somewhat quatrefoil shape with each leaf element intersecting the adjacent return passage 20.

Again referring to Figure 3, a rotatable valve spool assembly, including a valve spool 21, connecting bolt 22, and a reaction type jet motor assembly 24, is slidably enclosed in a valve sleeve 25 which will be described later.

The valve spool 2| has a center bore 26 entering one end thereof, running axially through its section and terminating approximately midway between the center of the spool 2| and the opposite end. The spool bore 26 has a threaded portion 21 adjacent the left end thereof, adapted to screw onto the threaded end 29 of the connecting bolt 22. A balancing land 30 is provided at each end of the spool 2|, contacting the inner surface of the valve sleeve 25 and acting to longitudinally support the spool. Return fluid is admitted to the return chambers l4 and I5, upon its return from the operating ports I! and I9, through a number of opposed slots 3| spaced around the periphery of the balancing lands 30. Inwardly from each balancing land 30 and toward the center of the spool 2 l, metering lands 32, precision ground to match the sleeve cylinder surface, are provided to progressively uncover a number of metering flow holes 34 in the valve sleeve 25 as the spool 2| is axially displaced in response to push-pull movement of a control rod (not shown) and will be described later. A pair of opposing pressure ports 35 are bored transversely through the wall of the valve spool 2|, midway between the metering lands 32, to direct a portion of the incoming pressure fluid into the spool bore 26.

The spool 2| terminates at its right end with a spindle 3'! adapted to enter a ball bearing 39 contained in an end bearing coupling 40 and with a circumferential groove in the connecting bolt 22. A lockv/ire 44 is retained in the spool groove dI, having a small portion of one end bent inwardly and projecting through a small bore 42 in the spool groove 4| engaging the groove 25 provided on the connecting bolt 22, locking the two units together, thus preventing their becoming unscrewed during rotation. An axial bore 48 enters the right end of the connecting bolt 22 and forms a chamber which connects with the spool bore 28. Two opposed orifices 41 extend through the Wall of the connecting bolt 22, adjacent the left end thereof, into an outer peripheral fiuid groove 49 on the connecting bolt 22. A hexagon collar 5c is provided on the connecting bolt 22 adjacent the fluid groove 49 to abut, position and retain the jet motor 24 against the left end of the valve spool 2| when the jet motor 24, connecting bolt 22, and spool 2| are assembled in the valve body IS. A packing seal groove 5i and an O ring seal 52 retained therein extends around the outer periphery of the connecting bolt 22 about midway between the ends thereof, preventing leakage between the spool 25 and the connecting bolt 22. A threaded spindie 54 at the left end of the connecting bolt 22 is adapted to pass through a ball bearing 55 contained in an end bearing coupling 55, and receive a lock nut 51.

It should be noted that the bearings 39 and 55 are preferably held as small as allowable by the load requirement, and are provided to minimize frictional drag which should be overcome by the jet motor 24.

The valve spool 2| is thus rotatably positioned in ball bearings between the two end bearing couplings and can rotate freely, irrespective of t axial movement of the spool.

The jet motor 24 (see Figures 5 and 6) is provided with a central body 59 having an axial center bore 238 adapted to press fit onto the connecting bolt '22 and abut the hexagon collar 50. A pair of opposed arms BI extend outwardly, and in line, from the jet body 59 perpendicular thereto, having central fiuid passages 82 entering the center bore 68 of the body 59.

When the jet motor 24 is positioned on the connecting bolt 22, the fluid passages I52 in the jet arms ti connect at the basal ends thereof with the fiuid groove 49 around connecting bolt 22 and orifices 4I. Fluid is thereby directed through the connecting bolt orifices 41 into the fluid groove 49 and out the jet arm passages 82.

The terminus of each arm 8% is sealed with a metal ball 64 silver soldered in place. A transverse jet bore 65 is bored at right angles to the passage in each arm 8| and at right angles to center bore 55 of the jet body 59; the jet bore of one arm diametrically opposing the jet bore in the other arm so that when the stream of pressure fluid is ejected from one arm 6| clockwise the stream of pressure fluid ejected from the opposite arm will be directed counter-clockwise, the reaction thereby rotating the assembly. The jet bores 65, of course, may be positioned to rotate the spool 2| in either direction as de- .sired, without substantially altering the efilciency of the valve.

Again referring to Figure 3, the right end of the valve body I9 is enclosed by a cap assembly 61 having a threaded portion 89 adapted to screw into the threaded portion of the return chamber I5 and abut the shoulder 89 of the valve sleeve 25, thus securing the sleeve 25 in the body cylinder I6. A peripheral groove 8|, retaining an 0 ring seal 82, extends around the exterior circumference of the cap 81 preventing external leakage. A bushing 84 is pressed into an axial bore 85 in the cap er, and the outer end of the bushing 84 has a counter bore 85 to receive an 0 ring seal 81 adapted to admit and seal an idler rod 88 which extends therethrough.

The left cap assembly 89 slidably fits into and encloses the left return chamber I4 and is locked into place by an internal nut 9|! screwed into the threaded portion 58a of return chamber I4. The inner end of the cap 89 has an annular groove 9| extending around the outer periphery thereof and an 0 ring seal 92 is retained therein to prevent external leakage. A bushing 94 is pressed into an axial bore 95 in the inner chamber 96 of the cap 89 and abuts a partition 91 which separates the inner chamber 95 from an outer chamber 99. A counter bore Inn on the inner end of the bushing 94 retains an 0 ring IOI, and an idler rod I92 is admitted and sealed therethrough. v

The outer chamber 59 of the cap 89 is cylindrically contoured to receive the enlarged barrel portion I95 of idler rod I92, having an elongated transverse bore I9? through its section adapted to receive an idler pin I534. The idler pin I04 extends through a pair of opposed bores I68 in the cylinder section of the cap 89 and fastens the idler rod I92 therein. The length of the elongated bore I07 in the idler rod I92 should be accurately determined to limit the axial movement or" the valve spool 2|.

The idler rod I82 extends through the cap 89 and bushing 84 and enters the large end portion of end bearing coupling 58 and is attached therein by means of a coupling pin :99. The coupling pin bores I98 in the end bearing coupling 56 are undercut and the coupling pin bore III through the idler rod I82 is counter-bored on each side, allowing sufficient play between the coupling pin I09 and the attached elements to prevent the valve spool 2| from binding in the valve sleeve 25.

Idler rod 88 passes through the right cap 61 and bushing 84 to be connected into the end bearing coupling 48 by means of a coupling pin IIII extending transversely through end bearing coupling bore H2 and idler rod bore II4. End bearing coupling bore I I2 and idler rod bore II4 are undercut and counter-bored respectively to prevent binding of the spool 2| as in the case of the right end as described above.

The exterior periphery of valve sleeve 25, as shown in Figures 3 and 7, is provided with pressure packings I20 and 0 rings I2I, retained Within groves I22 at each end thereof, preventing external leakage therein, Another set of grooves I24 inwardly of the pressure fluid grooves I25 at each end of sleeve 25 also retain pressure pack ings I29 and 0 rings I2I, sealing pressure fiuid grooves I25 off from the pressure inlet groove I28 provided around the center of the sleeve 25. The pressure inlet grove I28 is bored at spaced intervals around the circumference of the valve sleeve 25, providing pressure inlet ports I26 which ad:

mit pressure fluid to an inner chamber I21 between the valve spool 2| and valve sleeve 25 (see Figure 3). The pressure fluid is then distributed through the metering flow hole patterns 34 in the valve sleeve 25 in accordance with metering land positions and through valve spool ports 35 and into the inner valve spool bore 26 to be forced out the jet motor 24 and jet orifices 65.

Each set of metering flow holes 34, as shown in Figure '7, comprise a number of evenly spaced orifices I23 radiaiiy located in the fluid grooves I25 in a somewhat staggered fashion around the periphery of the valve sleeve 25. Each orifice I29 consists of a small drilled portion next to the interior cylinder I6 of the sleeve 25 and an outerdrilled portion facing the pressure groove I25. The flow holes I29 of each set 34 are staggered in the lengthwise direction of the sleeve 25 to provide a predetermined relationship between the valve spool 2| displacement and flow rate change. When the valve spool 2| is in neutral position, all of the flow holes in the pattern 34 are blocked with the exception of the two holes of each pattern which are the farthest apart and these are preferably bisected (as best shown in Figures 3 and 9), by the opposite edges of each respective metering land 32, so that a small neutral leakage value continuously exists to both sides of the hydraulic motor piston I30, as shown in Figure 9.

By making the metering lands 32 on the spool 2| just wide enough to cover the desired proportion of the metering flow hole pattern 3-5., and providing fluid pressure and return grooves I25 in valve sleeve on opposite sides of each metering lane the same set of metering holes 34 is used to meter the fluid away from the hydraulic motor cylinier, as well as back into the hydraulic motor cylinder when the spool 2| is moved to the corresronding position. No idle flow patterns 34 ex during flow of the fluid in either direction it all the flow takes place through the in. a1 flow holes I23. Since the hole I each pattern 34 is symmetrical about its CSHLGL, a symmetrical fluid flow through the valve is obt. I on each side of neutral (see Figure 9), tilv e is no diiference in the response or controlled surface in either direction.

In one preferred form, a pressure of 3,006 p. s. i. s inlet II and the bisected nortioned to provide a pressure In consequence, there is in position, as shown in Figure 9, a gneloao of p. s. i. on both sides of the motor cylin ton, thus any alteration of the position of the control surface, other than by pilot control, prevented.

Inasl uch as a strong shearing force can be exerted be 11 valve sleeve 25 and the valve spool 2! at the flow hole patterns 35, the possibility of jamming due to the entrance of small foreign particles therebetween is reasonably slight. It is wise, however, to harden the valve spool 2E and valve sleeve 25 surfaces to a Rockwell hardness of 3-60 to C-65, for example, and

g the same temperature ooeificient of expansion is preferably used to avoid sin-ding between operating temperatures of from 65 F. to 135 F. for example.

In operation of the valve, the jet motor 24 rotates the spool 2i continuously at all times and in all valve positions.

In Figure the valve spool 2| is shown fully displaced to the right of neutral, and the flow of pressure fluid is directed through the set of drop of v Q- ncutral. sp

metering flow holes 34 in line with cylinder operating port I9, and into cylinder chamber A actuating hydraulic motor piston I30 of hydraulic motor I3I to the left, which in turn forces fluid out of cylinder chamber B and through the set of metering flow holes 3 3 into return chamber I4, thence out pressure return outlet I2 to the reservoir (not shown).

In Figure 9, the valve spool 2| is shown in neutral position. Pressure fluid is present around the inner chamber I21 between metering lands 32. A portion of the pressure fluid is directed through the valve spool center ports 35 and out the turbine jet assembly 24, rotating the spool thereby. lhe balance of the flow is directed across the bisected metering flow holes I29 into return chambers i and I5, maintaining a substantially constant operating force thereby to both sides of the hydraulic motor piston I30 in the hydraulic motor cylinder I 3| of equal value.

In Figure 10, the spool valve 2| is fully displaced to left of neutral and the situation described in Figure 8 and above has reversed. The metering land 32 at the left has unblocked the set of metering flow holes 34 in line with supply port ll directing the flow of pressure fluid to chamber B, moving hydraulic motor piston I39 to the rigl: and forcing the fluid out of chamber A into right return chamber I5. The fluid is then returned to return chamber I4 through end slots of cap assembly 6? and return passages 2|).

It thus will be seen that the valve spool 2| rotates constantly, irrespective of its position, as shown in Figures 8, 9 and 10, as long as pressure exists in the hydraulic circuit, providing a consistently low and substantially constant pushpull operating force at all times.

It is, therefore, apparent that the present invention, having a constantly rotating valve spool assembly, offers a number of decided advantages over conventional type metering valves.

While the present valve has been described as being ideally suitable for use in a control system for aircraft surfaces, it will be readily seen that the advantages of the invention, as described herein, can be of value in other uses. Such uses within the knowledge of those skilled in the art are deemed to be included within the scope of the appended claim.

While in order to comply with the statute, the invention has been described in language more or less specific as to structural features, it is to be understood that the invention is not limited to the specific features shown, but that the means and construction herein disclosed comprise the preferred form of several modes of putting the invention into effect, and the invention is, therefore, claimed in any of its forms or modifications within the legitimate and valid scope of the appended claim.

What is claimed is:

A hydraulic valve structure of the kind described, including: a valve body having a cylindrical bore and a return chamber connected to an outlet conduit; a valve spool mounted in the cylindrical bore and provided with an axial bore in communication with pressure fluid passages in said valve body; a part extending axially from the valve spool into said return chamber and provided with an axial bore communicating with the axial bore in the spool; a reaction motor mounted on said axially projecting part in said return chamber and provided with pressure fluid through the bores in the spool and axially projeoting part; removable end caps closing each 1 the bore in the valve body; pressure reg bearings positioned in said end caps; rod nts supported for axial movement in said ,earings mounted co-axially with the valve spool; and anti-friction means within the bore of the valve body and connecting the rod element at one end of the valve body to the spool, and at the other end of the valve body connecting the rod element to the axially extending part on m I which the reaction motor is mounted.

WARDE L. PARKER.

References Cited in the file of this patent Number UNITED STATES PATENTS Name Date Herdman Apr. 18, 1899 Booth Feb. 8, 1927 Wilson July 24, 1934 Nichols July 19, 1938 Donaldson Dec. 15, 1942 Bertea Aug. 23, 1949 Gerst Sept. 5, 1950 Avery Aug. 28, 1951 Walthers Jan. 8, 1952 

